Current video coders, such as developed for example in the AVC H.264/MPEG-4 standard (“Advanced Video Coding”) of the ITU (“International Telecommunication Union”) presented in the document ISO/IEC 14496-10, make it possible to code an image sequence so as to deliver a coded sequence, compressed with respect to the source image sequence.
Accordingly, these coders use a discontinuous representation of the video sequence. More precisely, the images of the sequence are sliced up into blocks of pixels, a block of pixels corresponding to a grouping of adjacent pixels. These coders are based on a processing of the information contained in these blocks which involves a transformation step, a quantization step and an entropy coding step. Thus, each block is coded by intra-image or inter-image prediction.
A drawback of these prior art techniques is that the blocks in each image are defined independently of the blocks of the other images of the sequence. This gives rise to a discontinuous representation of the motion in the sequence, and therefore a poor representation of the real motion and cost overheads in terms of compression bitrate.
Alternative techniques, based on meshes for example, have thus been proposed, offering a continuous representation of the motion.
However, a drawback of these mesh based techniques is that the motions between the regions are constrained, and therefore do not make it possible to represent the breaks in the motion field that may arise in the image sequence (for example due to the appearances or to the disappearances of objects), between two regions having different motions.
Moreover, another drawback of these techniques stems from the use of irregular meshes, for which the structure of the mesh cells over the course of time must be transmitted. Indeed, this transmission of additional information gives rise to penalties in terms of compression performance.
There therefore exists a requirement for new techniques for coding/decoding images making it possible to at least partly alleviate the drawbacks of the prior art.